The onus is on the person that asserts something is real, not on the person making no claim, to prove something exists. And exceptional claims need exceptional proof to be verified. I fully accept that people have faith that God exists, but for a person like myself, who has little faith in things that are outside of the natural world and not supported by evidence outside of supposed personal experience (and unrepeatable and unmeasurable experiences at that), I see no reasons to have faith that God exists. I however do not have to have any real amount of faith to think God doesn't exist, at least not to the same degree that thinking God exists requires. Because I'm not that one making the claim that an extremely complex and omnipotent being created the universe. I'm making no claim at all beyond disbelief in the supernatural.
At the end of the day, Religion is based on faith. Which is perfectly fine if thats how you want to live and think. But faith thats blind has absolutely nothing to do with Science and should thus stay within its own scholarly disipline. This is the threat of Creationism. It attempts to inject faith into a place where it doesn't belong. Simple as that.
